It is a requirement in a large number of situations to provide a mounting whereby a component is resiliently fixed despite being subject to loads as a result of thermal cycling or mechanical pressures. Ideally, these loads should be accommodated in the form of relative slippage to avoid overstressing of the component.
FIG. 1 illustrates a typical prior mounting arrangement of a vane 1 secured between an inner mounting ring 2 and an outer casing 3. The vane 1 is secured to an inner platform 4 and an outer platform 5 from which a tang arm 6 extends to a tang 7 which is engaged in an interference fit with a slot or groove 8 formed in the respective ring 2 or casing 3. This engagement may be an interference or close clearance fit. Although illustrated with respect to a tang mounting arrangement it will be appreciated that other mounting arrangements and fixing mechanisms could be used. The vane 1 may typically be formed from an organic matrix composite aerofoil material. The vane 1 may be held in place in a bypass, fan or compressor module of a gas turbine engine. Alternatively, the vane 1 could be formed from relatively high temperature materials which would allow operation in the turbine stages of a gas turbine engine.
The arrangement depicted in FIG. 1 as indicated is typically used to anchor a vane in place in forward and rearward positions through insertion of tangs into circumferential slots in the casing 3 and inner ring 2. In such circumstances as can be seen there is a four point fixing arrangement constituted by the respective tangs 7 in the slots or grooves. There is a semi freedom for the respective tang 7 to slip, subject to any clearance gap and any interference friction within their respective slot or groove 8 in order to provide a mechanism for damping any vibration in the vane which may be induced by periodic variations in gas stream flow, such as due to blading, or structural vibrations transmitted through the inner ring 2 or casing 3. It will also be understood that the tang 7 may also provide a gas seal when required.
A particular problem relates to the fact that four-point fixing with the arrangement as depicted in FIG. 1 can cause over-constraint upon the vane 1. It is accepted that a structure needs three distinct displacement and three distinct rotation constraints in order to provide positional retention. In practice, there are also design clearances and thermal growth effects, etc., to consider, but it is broadly accepted that a fourth tang is largely redundant and, as indicated, provides over-constraint. In such situations vibration, thermal growth or direct loading of the component, that is to say the vane 1, can result in stress or strain distributions which give rise to constraint forces at the respective fixing points. With four fixing points these constraint forces are accentuated.
FIG. 2 illustrates a typical prior mounting arrangement whereby a vane 21 has a platform 11 which is secured to a tang element 27 by an adhesive layer 12. Such an arrangement is relatively easy to manufacture whereby the vane 21 and platform 11 can be formed and secured through the adhesive 12 to an appropriately shaped tang element member 27 with limited machining and other manufacturing processes necessary. Unfortunately, the constraint forces tend to limit the load potential of the arrangement as depicted in FIG. 1. It will be understood that the bonding provided by the adhesive layer 12 between the element 27 and platform 11 may be subject to straining forces or potentially more importantly the area, known as the tang arm, connecting the tang end of the element 27 with the remainder of that element will be subject to such loading. In such circumstances there is a possibility of peel failure between the element 27 about the adhesive layer 12, or failure of the tang arm.